Toners are used in the development of electronic pictures, electrostatic printers, copy machines, etc., and can be defined as paint that is capable of being transferred to and fixed on an object to form a desired pattern. As computers are more commonly used in word processing in recent years, there have been rapidly growing demands for image forming apparatuses such as printers, resulting in an increase of the amount of toners used as well.
Typically, toners are prepared by using a pulverization method or a polymerization method. The most widely known is a preparation method by using the pulverization, wherein resins and pigments are put into a melt-mixing process together, melt-mixed or extruded, and then pulverized and sorted to give toner particles. However, this method has drawbacks in that the toner particles thus obtained have a broad particle size distribution and very irregular shapes including sharpened edges resulting in inferior chargeability or flowability.
For the purpose of addressing the above-mentioned problems, a method for preparing spherical toner particles by using a polymerization method was proposed. For such a preparation method of toners by using polymerization, emulsion polymerization (coagulation method) and suspension polymerization are known in the art. The method for preparing toners by using the suspension polymerization is preferred since the emulsion polymerization has difficulties in controlling the particle size distribution and reproducing the quality of the obtained toners.
In the suspension polymerization, the binder resin monomer and various additives including a pigment, a wax, a charge control agent, an initiator, etc. are uniformly dispersed to provide a monomer mixture, which is then dispersed in an aqueous dispersion and subjected to a polymerization reaction to give particles having a diameter of about 6 to 10 μm that is appropriate as toner particles.
In the polymerized toner given by the suspension polymerization, a binder resin having a high molecular weight is contained as a monomer for the binder resin to be polymerized. Due to the binder resin having a high molecular weight, there is a problem that the gloss of prints is lowered. In order to solve such a problem, a method for realizing high gloss in prints has been proposed by adding a molecular weight control agent along with a variety of additives such as a wax, a charge control agent, etc. However, according to this method, the molecular weight of the binder resin is lowered to deteriorate the offset feature. Accordingly, there has been a need for research to develop a polymerized toner that not only may be prepared by a suspension polymerization method but that may also realize high gloss as well as an excellent offset feature.